When communicating between communication devices via a transponder mounted on a communications satellite, each communication device needs to maintain a communication line between the communication device and the transponder during the communication. For this reason, a conventional communication device maintains a communication line by tracking a transponder with a tracking antenna.
A tracking antenna tracks a communications satellite with high precision and always operates to face directly toward a communications satellite. However, there are cases in which the tracking antenna has a tracking error (error angle) alpha from a direction to be oriented depending on the level of fluctuation of the tracking signal in a transmission path or the performance of a receiver.
When the tracking antenna has a tracking error alpha, the tracking antenna, during transmission, radiates the strongest radio wave toward a direction shifted by the angle alpha from the tracking communications satellite. In this case, the radio wave radiating to the other communications satellite adjoining to the communications satellite to be tracked may become stronger than the radio wave radiated when the tracking error alpha is 0, interferes communication functions of the other communications satellite, and may block communication operations.
In order to prevent such an interference, the communication device includes a transmitting device that prevents from interfering other satellites, the transmitting device having an interlock function for blocking transmissions when the tracking error alpha of the tracking antenna exceeds a certain value.
Moreover, as a technique that automatically tracks a communication target to be tracked and that can avoid communication interruption, Patent Literature 1 discloses a system that tracks a directional antenna by combining the directional antenna and a non-directional antenna and exchanging information, such as the oriented direction, position information and the receiving condition of the directional antenna, between the transmitter and receiver using the non-directional antenna. Suppressing the tracking error alpha is theoretically possible by applying this technique.
However, in this system, only a range communicable with a non-directional antenna is a communicable area. Thus, in order to enlarge the communicable area, the transmission power via the non-directional antenna should be increased and this leads to an inefficient system. Therefore, it is not preferable to apply this technique to the satellite communication.